JPH0463252A - Nonoriented silicon steel sheet excellent in magnetic property - Google Patents

Abstract

PURPOSE:To obtain a nonoriented silicon steel sheet stably produceable without problems such as nitriding and internal oxidation and having low core loss and high magnetic flux density by specifying a compsn. constituted of Si, Mn, Al and Fe and regulating C, S, N and O as impurities. CONSTITUTION:This is a nonoriented silicon steel sheet having a compsn. contg., by weight, >2.0 to <3.5% Si, >1.0 to <2.0% Mn and >1.0 to <2.0% Al in such a manner that the total of Si(%) +Al(%)+0.5XMn(%) is regulated to <5.0% and the balance Fe with inevitable impurities, in which the content of C, S, N and O as impurities is each regulated to <=0.005% and excellent in magnetic properties. The steel sheet has low core loss and excellent magnetic flux density.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention is directed to a so-called high-grade non-directional film having a Si content of 2.0 to 3.5%. The present invention relates to magnetic steel sheets, and particularly to non-oriented magnetic steel sheets with low core loss and high magnetic flux density that are suitable for cores of large rotating machines such as large motors and generators.

(Prior technology) Non-oriented electrical steel sheets are often used in the iron cores of rotating machines such as motors, taking advantage of their small in-plane anisotropy in magnetic properties, and their magnetic properties include iron loss and magnetic flux. Emphasis is placed on density. Iron loss is the heat loss that occurs when magnetizing an iron core, and materials with low values result in less power loss in equipment.

Magnetic flux density indicates the degree of concentration of magnetic energy in the iron core, and materials with high values can make equipment smaller.

Large equipment generally requires higher quality materials with lower core loss than smaller equipment. This is because the amount of heat generated by iron loss is proportional to the volume of the core, while the amount of heat dissipated is only proportional to the surface area, so the larger the device, the more difficult it is to cool it. This iron loss is controlled by two factors: eddy current loss and hysteresis loss.

Eddy electric loss is a loss due to eddy current induced by magnetization, and depends on the resistivity and plate thickness of the steel. The thinner the plate, the lower the eddy current loss, but if it is too thin, the lamination work becomes complicated, so the JIS standard specifies three types of plate thickness: 0.65 mm 1° 0.5 mm and 0.35 m. ing. In terms of materials, the higher the specific resistance of the steel, the lower the eddy current loss (the lower it becomes), and the addition of alloying elements is generally effective.

In particular, Si has a large rate of increase in specific resistance per unit amount of addition.
Moreover, it is widely used because it is inexpensive. Also,
A1 and Mn have similar effects, so they are high class! It is often used in magnetic steel sheets. In the case of non-oriented electrical steel sheets, if the sheet thickness is the same, the eddy current loss is almost uniquely determined by the specific resistance value, so the amount of alloying elements such as S is also determined roughly depending on the grade. .

On the other hand, the hysteresis loss decreases as the number of fine precipitates and grain boundaries that impede domain wall movement during the magnetization process decreases. Therefore, the important point in manufacturing high-grade magnetic steel sheets is to use high-purity steel as the raw material and to grow the crystal grains. In terms of composition, the content of impurity elements that cause fine precipitates such as C, S, N, and O (#element) is kept as low as possible, and carbonitride-forming elements such as Ti, Nb, ■, and Zr are kept as low as possible. It is important to strictly limit contamination. Fine precipitates themselves not only hinder domain wall movement but also inhibit grain growth. AI also generates fine AIN and has a similar negative effect, so low-grade 1, which has a low Si content, is often not added to magnetic steel sheets, but it is added to high-grade magnetic steel sheets for the purpose of increasing specific resistance. . In this case it is usually 0
．． By adding a large amount of 1% or more, the precipitates are coarsened to avoid adverse effects on crystal grain growth. In addition to the growth of crystal grains, grain size adjustment is also important, and the larger the crystal grains, the lower the hysteresis loss. In order to promote grain growth, it is desirable to perform annealing at as high a temperature as possible, and in principle there is no limit to the annealing temperature for high-Si steels that do not undergo α/γ transformation. However, when a steel plate containing a large amount of Si, Mn, or AI is annealed at high temperatures, internal oxidation and nitridation tend to occur on the steel plate surface.
On the contrary, the magnetic properties may deteriorate. The addition of special elements such as sb and Sn is effective in preventing nitridation during high-temperature annealing.
Although methods such as adjusting the dew point of the annealing atmosphere and applying special substances to the surface of the steel sheet are effective ways to prevent internal oxidation, these methods are not necessarily sufficient.

By the way, all of the methods for improving iron loss described above are disadvantageous from the viewpoint of magnetic flux density. That is, when a large amount of an alloying element such as Si is added to reduce eddy current loss, the iron content decreases by that amount, and the magnetic flux density inevitably decreases. When crystal grains are grown to reduce hysteresis loss, a texture (crystalline orientation) that is unfavorable to magnetic properties tends to develop, and the magnetic flux density decreases.

It is known that controlling the texture is effective as a means of achieving both magnetic flux density and iron loss. Direction!
Magnetic steel sheets make maximum use of this method, and are not easily magnetized.By aligning the axes in the rolling direction,
This simultaneously improves iron loss and magnetic flux density in that direction. In the case of a non-oriented tM1 steel sheet, it is sufficient to increase the number of crystal grains with (100) planes parallel to the rolling surface, but so far no high-grade non-oriented electrical steel sheet that has achieved this industrially has appeared.

Japanese Unexamined Patent Publication No. 58-25427 discloses a method for manufacturing a non-directional magnetic steel sheet using texture.

This method uses high Al steel (AI) containing almost no Si.
:0.6~3.0%) is used in the material, a strong (100) texture develops through annealing, and magnetic flux density and iron loss are improved at the same time, but the material steel has a low Si content. Therefore, you get no direction! Magnetic steel sheets have relatively high iron loss levels.

In addition, Japanese Patent Application Laid-open No. 58-23410 discloses that steel containing 2.5% or more of 31 and 1.0% or more of slag is used, cold rolling is performed at a high reduction rate, and finish annealing is performed at a temperature of 1050°C or more. Non-directional with low iron loss and high magnetic flux density, performed at a temperature of 3 seconds or more but less than 60 seconds! A method of manufacturing a magnetic steel sheet is disclosed. However, in the case of this method, although the final annealing time is short, less than 60 seconds, there is a high risk that internal oxidation, surface flaws, etc. will occur if the process is carried out at such high temperatures.

(Problems to be Solved by the Invention) In view of the above circumstances, the present invention aims to provide a non-directional material with low core loss and high magnetic flux density, which is free from problems such as nitridation and internal oxidation, and which can be produced stably industrially. ! The purpose is to provide magnetic steel sheets.

(Means for Solving the Problems) In the process of investigating various effects of alloying elements on the magnetic properties of high-Si steel, the present inventors found that only when AI and 10 were added in combination, iron loss and magnetic flux density decreased. It was found that improvements were made at the same time.

The present invention based on the above knowledge is based on "Sl: 2.0% by weight%"
more than 3.5%, Mn: more than 1.0% and less than 2.0
%, Al: more than 1.0% and less than 2.0%, and contained so that the sum of Si (%) + ^1 (%) + 0.5 × Mn (%) is less than 5.0% However, the remainder consists of Fe and unavoidable impurities, and the content of C, S, N, and 0 as impurities is all 0.005% or less, and the non-oriented tMi steel sheet has excellent magnetic properties.''

The reason why the non-oriented IT magnetic steel sheet of the present invention having the above composition has low core loss and excellent magnetic flux density is due to the synergistic effect of AI and -n. Although the detailed mechanism has not yet been fully elucidated, it is thought that this is because AI and Mn have a favorable effect on the magnetic properties through texture formation during annealing after cold rolling.

In other words, it is said that the formation of the (1001 texture) is influenced by the crystal grain size before cold rolling, and hot-rolled sheets are annealed for high-grade products to control the crystal grain size before cold rolling. When a material containing only a large amount of AI has a large amount of crystal grains, the crystal grains become too large, and a material containing only a large amount of Mn becomes too small.
This is considered to be because when I and Mn coexist, the effects of these elements are canceled out, resulting in an appropriate particle size. It is also presumed that by adding a large amount of AI and Mn, AIN and MnS tend to become coarser, improving crystal grain growth and at the same time having a favorable effect on texture formation.

(Function) Hereinafter, 1! of the present invention! The effects of the alloying elements in the magnetic steel sheet and the reason why their contents are limited as described above will be explained.

Sl: Si is effective in increasing specific resistance and reducing eddy current loss, and the content is set to exceed 2.0% in order to obtain the iron loss necessary for a high-grade non-oriented electrical steel sheet. If Si is less than 2.0%, the iron loss will not be as low as the target.

On the other hand, if Si is contained more than necessary, cold rollability will be impaired, so the upper limit is less than 3.5%.

Mn: Mn is added to high-grade electrical steel sheets to prevent hot embrittlement caused by S, but the content never exceeds 1.0% except in special cases. In the present invention, Mn improves magnetic properties by texture control. Actively include more than 1.0% for the purpose of improving. If Mn is less than 1.0%, the desired effect cannot be obtained. However, adding more than necessary will cause the steel to become brittle.
In addition, the growth of crystal grains deteriorates, so the upper limit of the content is 2.
．． Less than 0%.

In addition to the above effects, Mn is also effective in increasing specific resistance,
Furthermore, it is an element that does not significantly impair cold rolling properties. Therefore, there is an advantage that the addition of a large amount of Mn can reduce the content of Si, which has a strong tendency to deteriorate toughness.

Al: Generally, high-grade electrical steel sheets contain 0.1 to 1.0% of AI for the purpose of increasing resistivity and coarsening the AIN, but in the present invention, it is contained at 1.0% to improve the texture like Mn. %. If AI is less than 1.0%, the desired effect will not be obtained, and if it is contained more than 2.0%, the steel will deteriorate and cold workability will be impaired.

In the present invention, the contents of Si, Mn and AI are set to be within the above ranges and satisfy the following formula 0.
%) + Al (%) + Q, 5XMn (%) < 5.0%...
■The sum of the left-hand side of this equation 0 is approximately proportional to the specific resistance of the rope,
This is an indicator of iron loss. In order to achieve the desired low core loss, the total must exceed 3.5%, which is
This is automatically satisfied if the contents of i, Mn and A1 are each within the above ranges.

However, even if the contents of Si, Mn, and A1 are each within the above ranges, if the total content exceeds 5.0%, cold rolling properties will deteriorate significantly, making it difficult to manufacture stably industrially. Become.

C, S, N, Q: These impurity elements form fine precipitates and deteriorate the magnetic properties, so each must be suppressed to 0.005% or less. S is 0.002% or less to reduce fine precipitates of MnS, N is 0.002% or less to reduce nitrides such as AIN, and 0 is 0.002% or less to reduce oxides. It is preferable to suppress it to 0.002% or less.

Note that, as in the past, it is necessary to minimize carbonitride-forming elements such as T1, Zr, Nb, and V that are inevitably mixed in. Further, even if B is contained in an amount of 0.005% or less, the effects of the present application will not be impaired.

Non-directional of the present invention having the above composition! A magnetic steel sheet can be manufactured by the following process.

[Material steel] - [Hot rolling process] - [Hot rolled plate annealing process] -
[Cold rolling process once or twice or more with intermediate annealing]-
[Final annealing process] The low core loss and high magnetic flux density non-oriented tM1 steel plate of the present invention is
Although it is possible to manufacture the above-mentioned steps without any complicated conditions, the desirable conditions for each step are as follows.

C hot rolling process] The slab heating temperature in the hot rolling process is 1100 to 12
The heating temperature should be in the range of 50°C, preferably in the range of 1150 to 1200°C. Low-temperature heating is better to prevent deterioration of magnetic properties due to fine precipitation of MnS, but if the temperature is too low, it will be difficult to secure the hot-rolling finishing temperature. Variations in magnetic properties within the coil increase, and surface flaws are more likely to occur. The higher the hot rolling finishing temperature, the better the magnetic properties, usually 800°C.
The above is appropriate. It is also better to have a higher winding temperature.
Since the pickling properties deteriorate, a temperature of around 600°C is appropriate considering these factors.

[Hot rolled plate annealing process] High quality! For magnetic steel sheets, after hot rolling, the hot rolled sheets are annealed to recrystallize the processed & 11 weave. It is better to set this temperature higher than 800°C, but if the temperature is too high, the crystal grains may become too coarse and the cold rollability may be impaired.
For hot rolled sheet annealing, the upper limit should be 1100"6".
Although this is done for the purpose of improving magnetic properties and surface properties, in some cases nitridation or internal oxidation may occur, resulting in the exact opposite result. For this reason, in the past, the non-oriented Nfn#4 plate of the present invention required careful attention to the annealing conditions, and was not necessarily able to be processed in a fully satisfactory state due to attempts to balance contradictory factors. Since it is easy to control the crystal grain size even when treated at a relatively low temperature, the crystal grain size can be controlled without having to be treated at a high temperature as in the conventional method.

[Cold rolling process] Cold rolling may be carried out once or twice or more with intermediate annealing in between. When using the -fold cold rolling method, the final plate thickness should be achieved at a reduction rate of 60 to 90%. Good. If iron loss is particularly important, it is better to use a two-sided cold rolling method that includes intermediate annealing.
Intermediate annealing is preferably performed under the same conditions as final annealing.

[Final annealing process]

The final annealing and the intermediate annealing are from 950 to 1050"C
It is better to perform the final annealing and intermediate annealing at a high temperature because the crystal grains become larger and it is effective in reducing hysteresis loss. In addition, the crystal grain size also becomes coarse, which is disadvantageous in terms of vortex collapse.The non-oriented electromagnetic steel sheet of the present invention can easily control the grain size, so it is possible to obtain the optimum grain size at low temperatures. can.

(Example) The sea bream having the composition shown in Table 1 was dissolved, and the following manufacturing process was carried out to obtain 0.
It was made into a thin plate with a thickness of 5 mm. The components of each steel were adjusted so that the specific resistance levels were almost the same.

For hot rolling, the heating temperature is 1150°C, and the finishing temperature is 850°C.
It was finished to a thickness of 2.3 mm under the conditions of 550°C and a winding temperature of 550°C. After pickling the hot rolled sheet, it was subjected to a heat treatment of soaking for 1 hour in a 100% H2 atmosphere, and then cold rolled to a thickness of 0.5+sw at a rolling reduction of 78%. The final annealing was a simulated continuous annealing in which the sample was held for 60 seconds in a 9°% Nz 10% H2 atmosphere.

After the final annealing, test pieces were taken from the L direction (rolling direction) and the downward direction (perpendicular to the rolling direction), and their magnetic properties were measured. The magnetic properties were evaluated using the average value in the L direction and the downward direction. Table 2 shows the test results.

(Hereinafter, blank spaces) From Table 2, it is clear that the steels of the present invention (statements 1 to 4) all have good magnetic properties.

In contrast, comparative steel (NO, 5) with low Sl and comparative steel (NO, 8) with Mn both outside the range defined by the present invention
116) is inferior to the steel of the present invention in both iron loss and magnetic flux density. Comparison 11 (Nl17), in which only Mn is outside the range defined by the present invention, has a relatively good magnetic flux density but poor iron loss;
11B), on the other hand, has good iron loss but poor magnetic flux density.

(Effects of the Invention) The non-directional iri11m plate of the present invention has low iron loss and high magnetic flux density, and can be industrially and stably manufactured without any special restrictions on the manufacturing method. The non-oriented ITM1 steel sheet of the invention greatly contributes to improving the performance of large motors, generators, etc.

Claims (1)

[Claims] In weight%, Si: more than 2.0% and less than 3.5%, Mn:
More than 1.0% and less than 2.0%, Al: more than 1.0%2
．． Less than 0% and Si (%) + Al (%) + 0.5×
Contains so that the total amount of Mn (%) is less than 5.0%,
A non-oriented electrical steel sheet with excellent magnetic properties, with the balance consisting of Fe and unavoidable impurities, and C, S, N, and O as impurities all being 0.005% or less